Output instability or drift over time leading to measurement inaccuracies has long been a major deficiency for gas sensors irrespective of what technology or methodology is used for their conception or realization. Output software correction may alleviate the problem somewhat but it is in many instances inaccurate and not even always applicable. It has long been the objective of many researchers in this field to overcome this problem fundamentally and for good.
Recently the present author in U.S. Pat. No. 8,143,581, the disclosure of which is specifically incorporated by reference herein, advanced the teaching of an Absorption Biased NDIR Gas Sensing Methodology which is capable of eliminating substantially all the NDIR gas sensor output drifts over time without the need for re-calibration. As it turns out, the solution to solving this output drift problems for gas sensors actually lies deeper than the availability of superior NDIR gas sensor types even though they can indeed be designed to be capable of maintaining measurement accuracy over time. The fact of the matter is that people have experienced gas sensor output instability for such a long time in the past that when output stable sensors really come along nobody believes it. Until such time that stable gas sensors become widely available and users begin to consider their performance as trustworthy and truly believable, the real need today must be viewed from a completely different perspective, which is to be able to come up with a fast, inexpensive and simple methodology that can easily check the accuracy of gas sensors and inexpensively re-calibrate them when they are found to be inaccurate.
In U.S. application Ser. No. 13/149,738, filed May 31, 2011, of which this application is a continuation-in-part application, the present author advanced the teaching of a novel Re-calibration Methodology for simply and easily re-calibrating Absorption Biased (AB) designed NDIR gas sensors without the need of standard gases. With the recent advent of the Absorption Biased (AB) gas sensing methodology for realizing NDIR gas sensors whose outputs are significantly drift-free over time and also the advent of a complementing methodology that can check and re-calibrate AB designed NDIR gas sensors simply and easily without the need of standard gases, one would think that the gas sensor industry at large, particularly the HVAC industry, would be relatively satisfied and happily go forward in growing its business. But, unfortunately, this is not the case at all. While the HVAC industry is still trying to deal with their old and on-going problem of sensor inaccuracies over time, already the industry is pushing forward in finding new and better solutions for optimizing energy expenditure and achieving superior comfort level for occupants in buildings. One rather obvious approach widely being investigated and considered everywhere today is the grouping of all sensors in a building together into a computer network. These sensors can actually interact and work with one another in an efficient manner with self-commissioning, self-tuning, self-diagnostic and correction, and even self-configuring features. By so doing the energy requirement for buildings can be reduced to an absolute minimum while the comfort level and safety for occupants in the buildings can also be greatly increased.
No doubt from the standpoint of computer networking hardware and smart software availability today, this approach is clearly workable. However, when all the sensors are to be left alone by themselves to interact with one another over time in buildings, the obvious question to ask is whether these sensors are indeed ready to take on this self-policing task of always staying accurate. In other words, who is there to check whether the outputs of some of these sensors are actually staying accurate over time and if not, what are the consequences for the maintenance status of the buildings and the comfort level and safety of their occupants? Thus, while computer hardware and system networking software may be ready for this futuristic approach to building controls, it is very clear that not all the sensors needed to perform perfectly in this approach are here today to meet the challenge. In particular, gas sensors such as CO2 and dew point might be relatively accurate over time but for how long before they become inaccurate? But would there be anybody or any mechanism scheduled in the networking controls system to perform the checking or re-calibrating tasks for them? To put it bluntly, until such time that all the required sensors in the networking controls system can be self-commissioning or in other words can render themselves capable of automatically staying accurate all the time, the futuristic building controls approach with the use of computer networking and relevant software to connect all the sensors in the system together working interactively simply will not work.
It is the object of the present invention to advance a configuration design and methodology for AB designed NDIR gas sensors such that they can become self-commissioning or in other words capable of automatically maintaining their measurement accuracy indefinitely over time after initial calibration. This invention is achieved via extending the previously disclosed Absorption Biased methodology of U.S. Pat. No. 8,143,581 and Re-calibration methodology without the need of standard gases (U.S. Ser. No. 13/149,738, Wong) for NDIR gas sensors.